1. Clinically Used Methods for Detecting Sperm Fertility Problems
The incidence of male infertility in couples desiring conception has been estimated to be as great as 15% to 40% (11). Despite the great strides that have been made in understanding and treating infertility, one of the greatest difficulties has been the lack of adequate means to diagnose the existence, and potentially the cause, of the male contribution to such infertility.
Methods for evaluating male infertility are currently limited to the assessment of a few general aspects of function (7,8) and these largely depend upon determining whether the sperm meets certain descriptive criteria. The most commonly relied-upon "classical" parameters of semen analysis are sperm number, motility and morphology, and ability to penetrate the cervical mucus (14). Unfortunately, when such parameters are analyzed by different laboratories, there are substantial variations in the results obtained (12,18,19). In addition, if samples of the same patient are tested repeatedly, the results can be substantially different, and the results can also vary considerably when tests from multiple samples of known fertile sperm are compared (20,21).
Even though such analysis has its problems, human male infertility can often be correlated with specific derangements in sperm characteristics. However, there is a subset of infertile men who have normal sperm parameters, yet repeatedly fail to fertilize oocytes in vitro. The lack of a method to detect such infertility leads to much frustration and expense, as such patients can only learn about it by repeated failures in efforts to undergo in vitro fertilization (IVF).
The need to find a more reliable indicator of male infertility has been a long-felt one, and has even encouraged some to evaluate the use of extremely complex methods of analysis. For example, some investigators have attempted to measure sperm movement characteristics using computerized systems that can reconstruct how sperm move (reviewed in Ref. 8). Investigators have also tried to apply an animal model that examines the motility of hyper-activated sperm as an indicator of fertilizing ability (1). Unfortunately, no more than 24% of all human spermatozoa incubated 3 to 24 hours conform to this animal model (22).
That even sophisticated methods of observing sperm numbers or mobility do not yield suitable tests for sperm fertility is not all that surprising, since more than 80% of infertile males have sperm counts which meet or exceed the "normal standards" (20), and since fertility only requires that a small fraction of sperm be functional (22,23). Observations of the sperm as a group is therefore not likely to be accurate.